| <?xml version="1.0" encoding="UTF-8"?> |
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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept rev="2.0.0" id="disable_unsafe_spills"> |
| |
| <title>DISABLE_UNSAFE_SPILLS Query Option (<keyword keyref="impala20"/> or higher only)</title> |
| <titlealts audience="PDF"><navtitle>DISABLE_UNSAFE_SPILLS</navtitle></titlealts> |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Impala Query Options"/> |
| <data name="Category" value="Performance"/> |
| <data name="Category" value="Scalability"/> |
| <data name="Category" value="Memory"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p rev="2.0.0"> |
| <indexterm audience="hidden">DISABLE_UNSAFE_SPILLS query option</indexterm> |
| Enable this option if you prefer to have queries fail when they exceed the Impala memory limit, rather than |
| write temporary data to disk. |
| </p> |
| |
| <p> |
| Queries that <q>spill</q> to disk typically complete successfully, when in earlier Impala releases they would have failed. |
| However, queries with exorbitant memory requirements due to missing statistics or inefficient join clauses could |
| become so slow as a result that you would rather have them cancelled automatically and reduce the memory |
| usage through standard Impala tuning techniques. |
| </p> |
| |
| <p> |
| This option prevents only <q>unsafe</q> spill operations, meaning that one or more tables are missing |
| statistics or the query does not include a hint to set the most efficient mechanism for a join or |
| <codeph>INSERT ... SELECT</codeph> into a partitioned table. These are the tables most likely to result in |
| suboptimal execution plans that could cause unnecessary spilling. Therefore, leaving this option enabled is a |
| good way to find tables on which to run the <codeph>COMPUTE STATS</codeph> statement. |
| </p> |
| |
| <p> |
| See <xref href="impala_scalability.xml#spill_to_disk"/> for information about the <q>spill to disk</q> |
| feature for queries processing large result sets with joins, <codeph>ORDER BY</codeph>, <codeph>GROUP |
| BY</codeph>, <codeph>DISTINCT</codeph>, aggregation functions, or analytic functions. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/type_boolean"/> |
| <p conref="../shared/impala_common.xml#common/default_false_0"/> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_20"/> |
| </conbody> |
| </concept> |